Field of the Invention
The present invention relates generally to surface plasmon resonance (SPR), and more specifically to assays utilizing SPR to detect protein-ligand interactions as well as compositions utilized is such assays.
Background Information
Voltage-gated sodium (Nav) channels constitute a welcome target for venomous animals seeking to disrupt the transmission of electrical signals to incapacitate prey or defend against predators. To this end, peptide toxins within these venoms have evolved to interact with a specific region within each of the four Nav channel voltage-sensing domains (VSDs), the S3b-S4 helix-turn-helix motif or paddle motif. The pharmacological importance of this distinct region was first recognized in voltage-gated potassium (Kv) channels where mutations in the S3b-S4 loop reduced channel sensitivity to hanatoxin, a founding member of the Kv channel gating modifier toxin family. Later, structural information revealed that the paddle motif makes few contacts with the rest of the channel protein, which prompted experiments in which the S3b-S4 region was swapped between voltage-gated ion channels without disrupting the voltage-sensing process. The paddle motif was also identified in each of the four Nav channel voltage sensors, and transferring these regions from mammalian or insect Nav to Kv channels resulted in functional Kv channels that are sensitive to an array of Nav channel toxins. One recurring outcome of these studies is that Kv channels containing the VSD IV paddle motif of donor Nav channels possess slower kinetics when compared with constructs containing paddle motifs from the other three VSDs. These observations fit well with the notion that VSD I-III activation in response to changes in membrane voltage is most important for channel opening, whereas VSD IV plays a distinct role in fast inactivating the channel after it has opened. As such, animal toxins that interact with the paddle motif in VSD I-III generally disrupt channel opening, whereas those that primarily target VSD IV commonly inhibit fast inactivation.